Poly(ethylene terephthalate) (also referred to as “PET”) is widely used in the manufacture of shaped articles such as a bottles, containers, compression or injection molded parts, tiles, films, engineered components, etc. Poly(trimethylene terephthalate) (also referred to as “PTT”) has recently received much attention as a polymer for use in textiles, flooring, packaging and other end uses. However, it has not found wide application in bottles, containers and other molded goods in spite of its having many superior properties compared to PET. For example, it has better thermal properties than PET, better electrostatic properties, and better barrier characteristics against water vapor, flavors and gases, characteristics which should be an advantage over PET in bottles and containers.
Essentially, the reason that PTT has not received wider use in these shaped article applications in spite of its excellent end use properties (e.g., in fibers) is that the preparation of shaped articles such as bottles and containers from PTT by compression, injection or blow molding requires high melt strength and/or melt viscosity, a property which has not been consistently achieved with the PTT polymers currently described in the art. Consequently, it is the purpose of this invention to provide PTT with increased melt viscosity and melt strength, useful in the preparation of shaped articles, in particular, bottles.
Japanese Patent Application Publication No. 56-146738 discloses bottles made from PET where no more than 20 mole % of the ethylene glycol used in its preparation can be replaced by other diols such as trimethylene glycol. Also disclosed is the use of 2 mole % or less of polyols and/or polycarboxylic acids such as trimethylolpropane, pentaerythritol, trimellitic acid, and trimesic acid.
Japanese Patent No. 3382121 discloses the use of polyols such as trimethylolpropane, pentaerythritol, glycerine, etc., and polybasic acids such as trimellitic acid, pyromellitic acid in preparation of polyester at the level of 0.1 to 5 mole % of the reactants. The diols disclosed for use in preparing the polyesters are ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, dimer diol, cyclohexanediol, cyclohexane dimethanol, and their ethylene oxide addition products. Japanese Unexamined Patent Publication 2003-12813 discloses the use of polyols and/or polybasic acids at a level of 1 mole % or less, preferably 0.5 mole % or less, as a branching component in PTT with improved moldability.
None of these references disclose PTT containing low levels of polyols or polybasic acids with the melt viscosity properties suitable for preparing shaped articles, particularly bottles.